Field of the Invention
The present invention relates to a motor driving device.
Description of Related Art
Conventionally, a brushless DC motor is used as a power source for various electronic equipment. The brushless DC motor includes a rotor with a permanent magnet having a plurality of magnetic poles and a stator having a plurality of slots around which coils are wound separately.
Further, the brushless DC motor is usually equipped with a plurality of Hall sensors arranged to correspond to the stators in order to detect position of the rotor with respect to the stator. As the Hall sensor, a Hall element or a Hall IC is used, for example. When controlling the brushless DC motor, a motor driving device applies a drive voltage corresponding to a position detection signal based on the Hall sensor to the motor, and hence current flows in the coils so that rotation of the motor is controlled.
However, conventionally, if even one of the plurality of Hall sensors becomes an abnormal state so that the position detection signal corresponding to the abnormal Hall sensor becomes abnormal, rotation of the motor cannot be controlled.
Therefore, JP-A-2009-201346, for example, proposes a motor driving device that can drive the motor to rotate even if an abnormality occurs in the Hall sensor.
However, JP-A-2009-201346 does not specifically disclose how to control rotational frequency of the motor when an abnormality occurs in the Hall sensor.